Ring Transformation of 2-Furylcarbamates to 5-Hydroxy-3-pyrrolin-2-ones. Effects of Substitution in the Benzene Ring on the N-Carbobenzyloxy-5-hydroxy-5-phenyl-3-pyrroline-2-one-cis-γ-Ketoamide Equilibrium

Abstract

In the ring transformation of 2-furylcarbamates (2) to 5-hydroxy-3-pyrrolin-2-ones (3) by irradiation in the presence of oxygen, there is an equilibrium between N-carbobenzyloxy-5-hydroxy-5-phenyl-3-pyrrolin-2-one (3-A) and cis-γ-ketoamide (3-B) ; this equilibrium was studied by nuclear magnetic resonance spectroscopy. The presence of electron-withdrawing groups in the benzene ring selectively stabilized the hydroxypyrrolinone tautomer, while that of electron-releasing groups had the opposite effect. These results indicate that the ring-chain tautomerism depends on the electronic and/or steric factors of substituents on the benzene ring.